RC4-MD5 String Crypter

Unit CipherRC4.pas

unit CipherRC4;

interface

uses
  SysUtils;

type
  RC4 = class
    protected
    private
    public
      class function Encrypt(Key, Text: String): String;
      class function Decrypt(Key, Text: String): String;
  end;

implementation

{ RC4 }

class function RC4.Encrypt(Key, Text: String): String;
var
  i,j,x,y: Integer;
  s: array[0..255] of Integer;

  charCode: Integer;

  ct: String;
  ctInt: Integer;
begin

  for i := 0 to 255 do
  begin
    s[i] := i;
  end;

  j := 0;

  for i := 0 to 255 do
  begin
    charCode := Ord(Char(Key[(i MOD Length(Key)) + 1]));
    j := (j + s[i] + charCode) MOD 256;

    x := s[i];
    s[i] := s[j];
    s[j] := x;
  end;

  // Reset variables
  i := 0;
  j := 0;

  ct := '';

  for y:= 0 to (Length(Text) - 1) do
  begin
    i := (i + 1) MOD 256;
    j := (j + s[i]) MOD 256;
    x := s[i];

    s[i] := s[j];
    s[j] := x;

    ctInt := Ord(Char(Text[y + 1])) xor (s[((s[i] + s[j]) MOD 256)]);

    ct := concat(ct, IntToHex(ctInt, 2));
  end;

  Result := UpperCase(ct);
end;

class function RC4.Decrypt(Key, Text: String): String;
var
  c,i,j,x,y: Integer;
  s: array[0..255] of Integer;

  copyText: String;

  charCode: Integer;

  ct: String;
begin
  for i := 0 to 255 do
  begin
    s[i] := i;
  end;

  j := 0;

  for i := 0 to 255 do
  begin
    charCode := Ord(Char(Key[(i MOD Length(Key)) + 1]));
    j := (j + s[i] + charCode) MOD 256;

    x := s[i];
    s[i] := s[j];
    s[j] := x;
  end;

  // Reset variables
  i := 0;
  j := 0;

  ct := '';

  if (0 = (Length(Text) and 1)) and (Length(Text) > 0) then
  begin
    c := 0;
    y := 0;

    while y < (Length(Text)) do
    begin
      i := (i + 1) MOD 256;
      j := (j + s[i]) MOD 256;
      x := s[i];

      s[i] := s[j];
      s[j] := x;

      copyText := Copy(Text,c,2);

      // Convert previous text
      charCode := StrToInt('$' + copyText) xor (s[((s[i] + s[j]) MOD 256)]);

      ct := concat(ct, String(Chr(charCode)));

      // Increasing loop counter
      y := y + 2;
      // Increasing copy counter
      c := y + 1;
    end;
  end;

  Result := ct;
end;

end.

Unit1 :

uses CipherRC4

//

// Crypt - Decrypt
procedure TForm1.Button1Click(Sender: TObject);
var
  ResultMd5: String;
  ResultRc4: String;
  Rc4Key: String;

  ValEncrypted: String;
  ValDecrypted: String;
begin
  // Edit1 has value that will be converted using some MD5 function. In our code, ResultMd5 has that value.
  if (Edit1.Text <> '') and (Edit2.Text <> '') then
  begin
    // Encryption Key
    ResultMd5 := 'de720e4e2f21470cb416785b6c2dc1be';

    Rc4Key := UpperCase(ResultMd5);

    ResultRc4 := RC4.Encrypt(Rc4Key,String(Edit2.Text));

    Memo1.Lines.Add('MD5: ' + ResultMd5);
    Memo1.Lines.Add('RC4 Encrypted: ' + ResultRc4);
    Memo1.Lines.Add('RC4 Decrypted: ' + RC4.Decrypt(Rc4Key,ResultRc4));

    ValEncrypted := RC4.Encrypt(Rc4Key,String(Edit3.Text));
    ValDecrypted := RC4.Decrypt(Rc4Key,ValEncrypted);

    Memo2.Lines.Add(ValEncrypted);
    Memo3.Lines.Add(ValDecrypted);
  end;
end;